Fix enchantment

[osuphobia]

Summary

Bugfixes "Fix enchantment"

Purpose of change

Fix #78735
Fix CI monster_throwing_sanity_test failure

Describe the solution

Fix enchant_cache::clear().

Describe alternatives you've considered

Use

enchant_cache tmp;
*enchantment_cache = tmp;

Testing

monster_throwing_sanity_test passed.
Tested rm13, phase immersion suit, and bio_night, all worked as expected.

Additional context

The old initial process

*enchantment_cache = inv->get_active_enchantment_cache( *this )

is equal to

enchant_cache tmp;
*enchantment_cache = tmp;

🤔
Maybe I can write a test case in another PR.